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Author Topic: 40D autofocus  (Read 13287 times)
ChristopherFrick
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« Reply #20 on: August 05, 2008, 09:37:10 AM »
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Hello all,

recently my EF-S 17-85mm IS lens started hunting madly on AF on my 40D. Personally I thought it was the lens as my EF-S 10-22mm is ok. But I didn't want to be without my 17-85mm being in the shop; so I started focussing manually. And you know what, I think I get better results.

By coincidence I came across this article this evening by Darwin Wiggett about AF.
http://www.naturephotographers.net/article...8/dw0408-1.html

Makes me go "hmmm".

Regards,
Chris.
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DarkPenguin
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« Reply #21 on: August 05, 2008, 10:02:05 AM »
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If this is new behavior you might want to check that there is no debris in the AF wells.  Just hit them (lightly) with a blower.  I've also used a visible dust style brush to use static to pull larger items (Goddamn cats.) out of the AF wells.

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Hello all,

recently my EF-S 17-85mm IS lens started hunting madly on AF on my 40D. Personally I thought it was the lens as my EF-S 10-22mm is ok. But I didn't want to be without my 17-85mm being in the shop; so I started focussing manually. And you know what, I think I get better results.

By coincidence I came across this article this evening by Darwin Wiggett about AF.
http://www.naturephotographers.net/article...8/dw0408-1.html

Makes me go "hmmm".

Regards,
Chris.
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« Last Edit: August 05, 2008, 10:08:45 AM by DarkPenguin » Logged
Ray
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« Reply #22 on: August 05, 2008, 08:10:16 PM »
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If a lens has any misfocussing behaviour, it's likely to be more apparent at wide apertures, especially as wide and wider than F2.8.

The problem might also be obscured by the fact that most lenses are not as sharp at full aperture as they are at F5.6 or F8, so it's easy to confuse a slight misfocussing for expected poor lens performance at full aperture. One then tries to avoid using the lens at full aperture, never realising that the noticeably softer result was largely due to a slight misfocussing.

In this respect, Live View is like a double-edged sword. It provides you with the facility to focus more accurately, but at the same time causes some consternation by highlighting the fact that some of your lenses are not autofocussing as accurately as you thought.
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ChristopherFrick
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« Reply #23 on: August 05, 2008, 09:03:02 PM »
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If this is new behavior you might want to check that there is no debris in the AF wells.  Just hit them (lightly) with a blower.  I've also used a visible dust style brush to use static to pull larger items (Goddamn cats.) out of the AF wells.
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I did all that and cleaned the contacts too. It worked (ie autofocussed) for a short time but then started having troubles again. Even upgraded the 40D's firmware which has a lens related fix, but to no joy.
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Ray
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« Reply #24 on: August 05, 2008, 09:49:14 PM »
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Even upgraded the 40D's firmware which has a lens related fix, but to no joy.
[a href=\"index.php?act=findpost&pid=213309\"][{POST_SNAPBACK}][/a]

The lens related fix in the most recent firmware doesn't appear to have anything to do with autofocus, though.

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What has been changed in verson 1.0.8 of the firmware?

It includes the following improvements and fixes:

Fixes a phenomenon in which Image Stabilization operation emits a sound when certain buttons are pressed, with the EF-S 55-250mm f/4-5.6 IS lens attached to the camera.
When pressing the shutter button halfway down or pressing the AF-ON button, the IS operation sound is normal. (This phenomenon will not affect the durability of IS unit parts)
Fixes a phenomenon in which the Image Stabilization operation emits a sound from the lens when IS lenses are attached to the camera.
Fixes a phenomenon in which a part of the image looks unnatural when reviewed on the LCD.
Depending on the color of the background, the edges of some objects in the image may appear to have a jagged edge and look unnatural. (Even if the image played back on the camera's LCD is affected by this phenomenon, the actual image data is not affected.)

Corrects errors in the Spanish and Norwegian menu screens.
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BruceHouston
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« Reply #25 on: August 05, 2008, 11:16:01 PM »
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This is slightly off-topic, and possibly well-known among the experienced.  But I have found that the best aid to focusing with my telephoto IS lenses (24-105 and 70-200), on or off tripod, is to half-press the shutter release to engage IS to keep the image still enough to focus on.  This is especially true using the 70-200 IS at 200 with teleconverter 1.4X on 40D (= 448mm equivalent).
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charleski
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« Reply #26 on: August 07, 2008, 07:18:34 PM »
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Lighter moments aside, there is something worrying about these posts concerning autofocus.  It could just be my usual old reactionary problem, of course, but I have to wonder about the current need that so many people believe that they have for autofocus in the first place.
[a href=\"index.php?act=findpost&pid=212940\"][{POST_SNAPBACK}][/a]
Whatever happened to split-prism focusing screens? So fast and easy to use. I used to love that on my Dad's Nikkormat. :/

I'd have to say I think the principal rationale for autofocus these days is the prevalence of APS-C SLRs. Smaller size and lesser brightness makes manual focusing a skill that requires much practice and experience. Since there is less light coming through the manufacturers can't use a decent matte screen to aid manual focus, making manual work even harder. After a couple of years of using a Canon 350D I played with my grandfather's OM2 and my jaw dropped.

When you have a *bright*, *big* image in your viewfinder that's coming from a matte screen which will accentuate sharpness when you get the correct focus, then manual focusing is intuitive. Unfortunately this is not true of the majority of dSLRs sold today. Maybe (hopefully) it will be in the future. Right now, though, autofocus is essential, as it will outperform all but the most skilled operators on current cropped cameras. Many of the complaints about autofocus are simply user error.
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Ray
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« Reply #27 on: August 07, 2008, 10:45:44 PM »
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Whatever happened to split-prism focusing screens? So fast and easy to use. I used to love that on my Dad's Nikkormat. :/

I'd have to say I think the principal rationale for autofocus these days is the prevalence of APS-C SLRs. Smaller size and lesser brightness makes manual focusing a skill that requires much practice and experience. Since there is less light coming through the manufacturers can't use a decent matte screen to aid manual focus, making manual work even harder. After a couple of years of using a Canon 350D I played with my grandfather's OM2 and my jaw dropped.

When you have a *bright*, *big* image in your viewfinder that's coming from a matte screen which will accentuate sharpness when you get the correct focus, then manual focusing is intuitive. Unfortunately this is not true of the majority of dSLRs sold today. Maybe (hopefully) it will be in the future. Right now, though, autofocus is essential, as it will outperform all but the most skilled operators on current cropped cameras. Many of the complaints about autofocus are simply user error.
[a href=\"index.php?act=findpost&pid=213760\"][{POST_SNAPBACK}][/a]

I agree completely. I have difficulty manually focussing whilst looking through those small viewfinders. But to be fair, we now have Live View on the current crop of DSLRs which does aid manual focussing a lot when the camera's on a tripod. However, trying to manually focus a 10x enlarged image on an LCD screen with arms outstretched is tricky.

My own problems with autofocus accuracy seem to be related to the nature of the target. Low light and a lack of contrast, as one would expect, make autofussing difficult and sometimes impossible. What surprise me, however, is that even in bright light, autofocus can be inaccurate on my 40D with a normally soft target such as a human face.

Well lit text, however, presents no problems.
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Rob C
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« Reply #28 on: August 08, 2008, 05:09:34 AM »
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What surprise me, however, is that even in bright light, autofocus can be inaccurate on my 40D with a normally soft target such as a human face.

Well lit text, however, presents no problems.
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Ah Ray, thatīs because a machine focuses with its cold mechanical heart whilst humans (I trust) focus on faces and other bits with both eye and emotion.

Rob C
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Ray
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« Reply #29 on: August 09, 2008, 03:44:26 AM »
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Ah Ray, thatīs because a machine focuses with its cold mechanical heart whilst humans (I trust) focus on faces and other bits with both eye and emotion.

Rob C
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On the other hand, it could simply be that autofocussing on the cheaper, cropped format cameras is only as good as the price allows. The fact that these cameras cannot autofocus when the maximum aperture is F8 (using a 1.4x extender on an F5.6 lens), tends to imply that autofocussing is not as accurate at wider apertures as the 1 series cameras are, which can autofocus at F8.

As regards the benefits of both eye and emotion, we now have P&S cameras that not only can recognise a face in a scene and focus on it, but can recognise a smile and closed eyes and not take the shot when the subject is either not smiling or is blinking.

Now, I'm smart enough to not press the shutter when the subject is not smiling, when a smile is required, but I'm not always quick enough to avoid pressing the shutter when the subject is blinking.  
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Ray
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« Reply #30 on: August 09, 2008, 04:16:55 AM »
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This is slightly off-topic, and possibly well-known among the experienced.  But I have found that the best aid to focusing with my telephoto IS lenses (24-105 and 70-200), on or off tripod, is to half-press the shutter release to engage IS to keep the image still enough to focus on.  This is especially true using the 70-200 IS at 200 with teleconverter 1.4X on 40D (= 448mm equivalent).
[a href=\"index.php?act=findpost&pid=213327\"][{POST_SNAPBACK}][/a]

Yes. That does help a lot when manually focussing with Live View. However, my fastest lenses, the 50/1.4 and 50/1.8 don't have IS. A camera like the 40D is amazingly light and compact with the 50/1.8 II lens; ideal for candid night shots without flash.

I bought the 17-55/2.8 partly for this reason and also because of an impressive test report at Photozone. According to Photozone's tests, the 17-55/2.8 is actually slightly sharper at certain focal lengths at full aperture than both the 50/1.4 and 50/1.8 primes are at the same aperture of F2.8, including 17mm, which is surprising considering Canon's poor reputation for wide angle lenses. My own tests have confirmed that all 3 lenses are about equally sharp at F2.8 when correctly focussed.

There's another problem manually focussing with Live View. With fairly wide angle lenses, it's necessary to magnify the image 10x (with my eyesight, anyway). That often entails going back to full screen mode after focussing to recompose the scene before taking the shot. One can easily lose the shot stuffing around like that, especially when the subject is moving even slightly.
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Rob C
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« Reply #31 on: August 09, 2008, 04:33:11 AM »
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Now, I'm smart enough to not press the shutter when the subject is not smiling, when a smile is required, but I'm not always quick enough to avoid pressing the shutter when the subject is blinking.  
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Then you have the wrong blinking subject! Sorry, just couldnīt resist that cheapo one.

I would hate to have a camera decide when it releases itself - how bloody arrogant of the makers and how limiting for the photographer. I think that some a/f systems wonīt allow release of shutter until max. focus has been attained, another instance when machine controls the human. It seems to me you are far better getting a slightly unsharp image of something that might be of great consequence than nothing at all because some arbitary notion of sharpness and its importance has ben decided in another brain than the camera operatorīs. I suppose that these systems have a switch-off function so that you can override them, but I feel that that kind of "function" is basically worthless and nothing more than another sales gimmick: a feature nobody really needs but adds to the list of other useless so-called advantages which can be factored in to raise the apparent market value and price, yes, mostly price.

Rob C
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Ray
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« Reply #32 on: August 09, 2008, 09:37:28 AM »
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I would hate to have a camera decide when it releases itself - how bloody arrogant of the makers and how limiting for the photographer. I think that some a/f systems wonīt allow release of shutter until max. focus has been attained, another instance when machine controls the human. It seems to me you are far better getting a slightly unsharp image of something that might be of great consequence than nothing at all because some arbitary notion of sharpness and its importance has ben decided in another brain than the camera operatorīs. I suppose that these systems have a switch-off function so that you can override them, but I feel that that kind of "function" is basically worthless and nothing more than another sales gimmick: a feature nobody really needs but adds to the list of other useless so-called advantages which can be factored in to raise the apparent market value and price, yes, mostly price.

Rob C
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I presume also that such features are an option and can be deselected. I mention it only because it's interesting that this sort of thing can now be done, as you wrote, by a machine with a cold mechanical heart.

One might even be able to use the feature to extract a wider, more appealing smile from a pretty girl. "Sorry darling, the camera won't take the picture until you smile. Sorry! the camera doesn't recognise your smile; a bigger smile, please. Ah! that's better."  
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wildlightphoto
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« Reply #33 on: August 09, 2008, 04:25:06 PM »
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I can bloody well use my own eyes when my subject sits still long enough for me to do so, but I rarely find warblers at 700mm to be so cooperative. 


Yellow-rumped Warbler photographed with 560mm f/6.8 lens x 1.37x crop factor = field of view of a 767mm lens on a full-frame camera, focussed manually:



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Even then the focus control is so coarse that the slightest twitch of the focus ring sends the lens right through the cm or two depth of field;

An artifact of the AF system.
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Why should we spend precious mental energy doing something as rudimentary as focusing when it can be done automatically?
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Focussing isn't rudimentary for me, it's critical, too critical to be left to a system that can only be used at specified points on the viewscreen and fails entirely at smaller apertures.

I find that two features missing from most modern photo equipment are critical to easy manual focus:  good viewfinders and good ergonomic design.  For viewfinders you'd have to go back to the Leicaflex SL of 1968 to see how good they can be.  The lack of good ergonomic design is obvious in the manual focus rings that are too course and too loose and poorly placed to balance the lens in the hand, and the tall tripod feet on long lenses that are supposed to double as a carrying handle but serve to magnify camera vibration when on a tripod and prevent the user from supporting the lens with his hand while focussing.  An incredibly poor design.
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Ray
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« Reply #34 on: August 10, 2008, 11:03:19 PM »
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Yellow-rumped Warbler photographed with 560mm f/6.8 lens x 1.37x crop factor = field of view of a 767mm lens on a full-frame camera, focussed manually:


An artifact of the AF system.
Focussing isn't rudimentary for me, it's critical, too critical to be left to a system that can only be used at specified points on the viewscreen and fails entirely at smaller apertures.

I find that two features missing from most modern photo equipment are critical to easy manual focus:  good viewfinders and good ergonomic design.  For viewfinders you'd have to go back to the Leicaflex SL of 1968 to see how good they can be.  The lack of good ergonomic design is obvious in the manual focus rings that are too course and too loose and poorly placed to balance the lens in the hand, and the tall tripod feet on long lenses that are supposed to double as a carrying handle but serve to magnify camera vibration when on a tripod and prevent the user from supporting the lens with his hand while focussing.  An incredibly poor design.
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Good post! I tend to sympathise with you. Autofocussing on small birds in foliage can also be problematical if there are twigs and leaves in close proximity to the bird. The autofocus system can so easily focus on a leaf just next to, but in front of, the warbler's head.

Good autofocussing bracketing might be the solution. There's no getting away from the fact that autofocussing, if accurate and fast, is vastly superior to manual focussing. However, if it's not accurate, it's essentailly useless.
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Rob C
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« Reply #35 on: August 11, 2008, 10:44:43 AM »
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Quote from: telyt,Aug 9 2008, 09:25 PM


Focussing isn't rudimentary for me, it's critical, too critical to be left to a system that can only be used at specified points on the viewscreen and fails entirely at smaller apertures.

I find that two features missing from most modern photo equipment are critical to easy manual focus:  good viewfinders and good ergonomic design.  For viewfinders you'd have to go back to the Leicaflex SL of 1968 to see how good they can be.

[a href=\"index.php?act=findpost&pid=214131\"][{POST_SNAPBACK}][/a]
/quote]







Telyt

As I said ealier, focussing is anything but rudimentary - itīs one of the sensual pleasures of photography.

Lovely colours on that bird - an example of Leicaīs special qualities or of your ability with computers?

Nikonīs  viewfinders on the F to F4 were pretty good too (I donīt know about later models); the cheaper FM and FM2 were not so hot - not even 100%, something which annoys me with the D200 and which seems absurd in ANY reflex system, regardless of price. Probably just another deprivation designed into the package to make you want to spend more...

Rob C
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wildlightphoto
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« Reply #36 on: August 12, 2008, 11:15:07 PM »
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Lovely colours on that bird - an example of Leicaīs special qualities or of your ability with computers?
I don't do much computer work on my photos: basic color balance, no noise reduction, minimal sharpening, that's about it.  This was with the DMR, I think ISO 800.
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The View
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« Reply #37 on: August 13, 2008, 06:00:32 PM »
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Why should we spend precious mental energy doing something as rudimentary as focusing when it can be done automatically?
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I think so, too.

Many have that feel, that, coming from a manual focus camera, they are giving something up when they let a computer chip focus for them.

We may be giving something up, but nothing we couldn't do if we wanted to.

And, actually, we don't really let the camera decide on what to focus on. We decide with the auto focus points.


Focus problems: I messed up a few shots in the beginning, when I had IS on while shooting at higher speeds. When you shoot quickly and move the camera, the IS may not be ready for every shot and still be working while you are already pressing the release.
« Last Edit: August 13, 2008, 06:06:54 PM by The View » Logged

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wildlightphoto
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« Reply #38 on: August 13, 2008, 06:41:51 PM »
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And, actually, we don't really let the camera decide on what to focus on. We decide with the auto focus points.

Unfortunately my subjects don't respect the AF points so I'd rather be able to focus at any point in the picture.
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The View
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« Reply #39 on: August 13, 2008, 07:35:05 PM »
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Unfortunately my subjects don't respect the AF points so I'd rather be able to focus at any point in the picture.
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You are misunderstanding my post.
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